1. Field of the Invention
The present invention relates generally to vehicle frame structures. More specifically, the invention relates to vehicle subframe structures for front suspension systems.
2. Background and Summary of the Invention
In order to increase the structural stiffness of a vehicle frame assembly, one or more subframes are rigidly attached between the left and right frame rails of a vehicle. A vehicle frame will commonly include a front subframe located beneath the engine. The vehicle frame rails extend in a longitudinal direction to the vehicle body while the front subframe spans between the left and right frame rails in a transverse direction to the vehicle body. The front subframe is commonly used as a mounting structure for vehicle suspension components.
Because of the weight of the engine and loads from the front suspension system, the vehicle frame rails have a tendency to roll inward. If the frame rails are allowed to roll, a reduction in the effectiveness of the vehicle suspension and steering systems will result. By rigidly connecting a front subframe to the left and right frame rails, greater resistance to frame rail roll is effected. In order to increase the stiffness provided by the front subframe, a cross member may also be included in the vehicle frame assembly. The cross member is also rigidly attached to and disposed between the left and right vehicle frame rails near the front subframe. Although the addition of a cross member results in a more rigid frame assembly, there are deficiencies with this design.
The vertical mounting location of the lower control arm is dictated by the front suspension system design and vehicle ground clearance requirements. In order to provide the required clearances, the attachment points of the lower control arms must be a sufficient vertical distance below the vehicle frame rails. However, as the vertical distance between the attachment point of the lower control arm and the center line of the vehicle frame rails increases, the resulting bending mount on the subframe increases. As the bending moment applied to the subframe increases, a proportional increase in the inward frame rail roll results. Therefore, there is a demand for an improved front subframe which allows for suspension component attachment while also providing increased strength to the vehicle frame assembly.
Another deficiency with the conventional frame-assembly design is in the event of an offset front end collision. Current frame assembly designs that include a front subframe have a tendency to distort diagonally in the event of an offset front end collision. In the event of a disproportionate load distribution between the frame rails having a subframe that is attached to each frame rail at one point, the subframe and frame rails will pivot about the single attachment point instead of transferring the load. When an impact occurs that results in a disproportionate amount of force distributed between the two frame rails, such as an offset front end collision, the frame rail receiving the greater amount of force will be thrust in the direction of the force. The result is that frame rail receiving the greater amount of force will be translated further than its counterpart. Therefore, the frame assembly distorts diagonally instead of transferring the load.
The addition of a cross member does not remedy the situation since the point where the cross member is attached to the frame will also pivot. Greater resistance to distortion is achieved by the addition of the cross member, but current frame assemblies are in need of improvement.
Accordingly, it is an object of the present invention to provide a subframe which includes a unitary front cradle that by design improves frame assembly function by reducing frame rail roll.
It is a further object of the present invention to provide a subframe which includes a unitary front cradle with a plurality of attaching points to provide additional stiffness in the event of a front end collision.
It is still another object of the present invention to provide a subframe which includes a unitary front cradle that provides means for deflecting objects in the path of the vehicle.
Accordingly, the present invention provides a frame assembly having a pair of frame rails and a subframe. The subframe has a generally U-shaped cradle that includes a front cross member and a pair of side members extending from the front cross member wherein the side members are angled downward from the front cross member. The front cross member and pair of side members are formed as a unitary (one-piece) cradle. A pair of attachment members extend in a generally vertical direction from the front cross member whereby the unitary cradle is adapted to be attached to the vehicle frame rails at the front cross member by the pair of front attachment members. A pair of rear attachment members extend in a generally vertical direction from a rear portion of the side members whereby the cradle is also adapted to be attached to the vehicle frame rails at a rear portion of the side members by the pair of rear attachment members. A pair of lower control arm mounts are suitably attached to a rear lateral portion of each pair of side members. A rear cross member is suitably attached at a rear portion of the side members and is removable. A steering gear is mountable to the rear cross member and a stabilizer bar mount is suitably embodied at a front portion of the unitary cradle.
A skid plate may be attached to a bottom surface of the unitary front cradle.
From the subsequent detailed description taken in conjunction with the accompanying drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.